Production of thorium



Jan. 9, 195i W. c. LILLIENDAHL 2,537,067

PRODUCTION oF 'moRIuM Filed April 24, 194e 62755451? WEE Patented Jan. 9, 1951 NETED STATES TENT` OFFICE PRoDUc'rioN or 'rHoarUM Vania Application April 24, 1946, Serial No. 664,583

(Cl. 'Z5-84) 1 Claim.

This invention relates to thorium, more particularly to the production of metal of an exceptionally high degree of purity, and to an improved method for the manufacture thereof.

The principal object of my invention, generally considered, is to produce thorium by reaction of a mixture of the chloride and oxychloride or one of said compounds with calcium, said reaction taking place in a cup enclosed in a container, said container being filled with an inert gas, as distinguished from the prior practice of reducing the oxide in a heavy-walled iron bomb with a ground-in stopper, said bomb being heated in open air.

Another object of my invention is to produce thorium powder by heating a compound, or mixture of compounds of thorium, and calcium by high-frequency induction, the reaction cup being enclosed in a bell jar of high-silica glass, that is, one of 96% silica glass, or one of quartz or similar material.

A further object of my invention is to treat the powder produced in accordance with the above, to consolidate it into coherent metal and to form to the desired shape.

Other objects and advantages of the invention will become app-arent as the description proceeds.

Referring to the drawing:

Fig. 1 is a diagrammatic view, with parts in section, of apparatus for producing thorium in powder form.

Fig. 2 is a vertical sectional view of apparatus for leaching the contents of the cup used in the reduction of the thorium compounds, to remove the thorium powder produced therein.

Fig. 3 is a vertical sectional View of apparatus for washing the thorium powder produced,

Fig. 4 is an elevational view of apparatus, with parts in vertical section, illustrating how the powder produced may be washed and dried.

The reduction of rare metal oxides, including thoria, by calcium or other reducing agents, has previously been accomplished in heavy-walled iron bombs, with a ground-in stopper held in place by a screw cap. Such devices have a number of limitations and disadvantages, to wit:

It is difficult to maintain an air-tight joint between the stopper and bomb and to prevent reoxidation of the thorium powder produced as the bomb cools, or during the heating process, Considerable warping of the bomb occurs during heating and cooling, thus necessitating time-consuming lapping operations between runs. The construction of bombs has been limited to materials which will resist oxidation at elevated temperatures, and iron or iron alloys have generally been used for economy. Bombs were without exception of heavy-walled construction to permit suicient surface area for sealing and presumably to withstand pressure produced in the reaction.

From thermo-chemical data and a consideration of the products formed in the reaction between thorium oxide and calcium, it was coneluded that the pressures developed in the reaction were insu'icient to necessitate the heavywalled bombs previously used. These conclusions were tested by placing an open iron cup under a high-silica, glass (or quartz) bell jar, evacuating the bell jar, and then heating the iron cup by high frequency induction to cause the calcium to reduce the thorium oxide. Vaporization of the calcium was suppressed by lling the jar with argon gas at a pressure slightly less than atmospheric. There was no abnormal pressure produced during the reaction, very little vaporization of calcium, and satisfactory thorium metal was obtained. Such invention is covered by application Serial No. 574,130, filed January 23r i945, now Patent No. 2,446,062, dated July 27, 1948.

An object of the present invention is to produce thorium metal by the reduction of chlorine compounds of thorium, such as thorium chloride, thorium oxychloride, or a mixture of said compounds, With calcium. The advantages of using these compounds either alone or as mixture will become apparent as the description proceeds.

In the reduction oi thorium oxide with calcium, the reaction is only slightly exothermic so that the temperature attained during reduction is dependent almost entirely on the external heat supplied by the high frequency coil. This results in a relatively ne powder. On the other hand, the reaction between thorium chloride and calcium is very exothermic resulting in high localized temperatures in the reaction cup, thus producing a` considerable coarsening eiect on the final powder produced. This is desirable in subsequent operations such as washing, drying, storing and pressing. Furthermore, the product of the reaction, in the case of thorium chloride, is calcium chloride which is fluid at the temperatures attained during reduction. This acts as a flux to obtain more fluid conditions in the cup, assists in melting the calcium, and thus increases the activity of the reaction.

If the amount of ThOCli` is relatively low in the salts used, the calcium oxide formed is dissolved in the calcium chloride formed, thus uxing the calcium during the reduction.

In producing thorium by this process, thorium chloride, or a mixture of thorium chloride and oxychloride are desirably prepared. For such preparation, various reactions are described in the literature, i. e.passage of; chlorine over a mixture of carbon and thorium oxide; chlorine admixed With sulfur monochloride over thorium oxide; carbon, tetrachloride overheated thorium oxide; anddehy'drationof thorium chloride-with ammonium chloride at 500 C. All of these refactions will produce thorium chloride with vary.`

ing amounts of thorium oxychloride.

In the preparation of thorium chloride, a convenient starting compound is-.the nitratefw'hicha may be dissolved in water andr'thorium precipitated as the hydroxide with ammonia. This isV then ltered, washed With water, and dissolved in hydrochloric acid. The thoriumis then'repre to pass throughy a, 1/wy mesh screen and mixed therewith. Mixing is preferablydonelinan airconditioned room, because of the hygroscopic character of the salt.

In-iFig. lgthere is shown apparatus'foreffecting the reduction of the selected thorium compound to metal. formed of a suitable metal, relatively inert to thorium at*I elevated' temperatures, preferably,

molybdenum, although a molybdenum-linedV iron cup, or one formed ofjiron or` steelmay be employed; However, if vthorium of'a very` low, iron content isdesired, molybdenum `or its equivalentV must" be used.' The. cup is supported; above a metal plate I2v which is preferably cooledjby circulating water therethroughbyv vmeansrof'inlet pipe I3.` and'outletpipa Mi The cuppreferably rests on a hollow refractory insulator A mix,- ture ofjthe selectedjhorium. compoundj or, cornpoundsand granulatedjdistilled calcium (5j to 10j meshlisplaced in thecup. A molybdenum cover 201s desirably placedpntop of"the,cup, topre, vent dusting ofj'thecharge during evacuation, reduce depositonpof."calcium onthe Vycor 101.11101 duringv the reaction,v and produce moreuniformV heatingl conditions Vwithin the cup. Arpreferred,

mixture is '70.gramsof the.70% thorium, chloride, thoriumoxychloride mixture, kand 34 gms. of

calcium,which representsanV excess of approxi-v, mately 98% or 100%; over that theoretically re.

quired', in accordancewith theu equations;

This weightY of calciumv is preferred;'although'sat isfactory,v metal has been produced with as low `as75% excess. As previously mentioned', it` is desirabler to produceV asuidfa condition offthe charge aspossible during," thel reduction, and-increasing -the excess-Dicalcium promotes this condition. The suggested '70%' thorium chloride,l 30% thoriumoxychloride mixture ispreferred onlybecause-it--is diiculttomake yandstore 100% thorium'chloride'.-

This involves a cup or crucible I l" The metal plate I2 is tubulated, as indicated at I6, and connected to a high vacuum exhaust system which may conveniently comprise a high vacuum pump, a mercury diiusion pump, and a liquid air trap Il. A 96% silica, bell jar or bulb t8, just large enough to slip over the cup, is set on, the metal baseand sealed-vacuum-tight, preferably by meansvof vacuum wax I9. The jar is then exhausted to a high vacuum through valve or stop cock 2l, a Geissler tube 24 serving, by failurefo a; discharge, to indicate the degree of exhaust desirably obtained.

Argon gas 1-(9927 %')fis then admitted to the bell jarz; lfas; from tank 25 through valve 2| to a pressurel of'Y about three quarters nof' an atmosphere. A mercury column 22 indicates this pressure, A gas-trapor blow-off 26, comprising a mercury column, is provided to sweep out the argon line to cock 2l prior to filling the system. The metal cup II is then slowly heated to from 11005?. C; to l200'C. for about 15-minutes, by energizingethev coilv 23 by high-frequency'electricalv power,l tov lmelt thefcalcium and reduce the.

thorium compoundito metal powder.-

Under the conditions speciiied;' the reaction appearsto start; atV atemperature of approxi-l mately 500" C. to-600' C.' Moderate pressuresareproduced-'byH the heat of fthe reaction so-that itwvasefound advisable-to partially evacuate the-l container during the-coursegof,V the reactionv to maintain a-posit'ive pressuren onthe outside of the bell-jar, thatfisjrom five to ten centimeters -Y of mercury, and insure a goodlseal. The'apparatus is then allowed to cool.

After the cup and` chargeA have thoroughly cooled, the cup is removed 'and'placedin-a-,ja-r' ord receptacle 2T; containing water and acetic,acid which dissolves4 the excess calcium,V calcium chloride,v and calcium loxide; formed in the reaction, as represented'in-Fig. 2. While inthe receptacle 27, thel cup U is preferably centered, as

byvrneans ofra block of wooclihand cooled during` 200cc. at av time,l until. approximately one literA .been added; stirring continuously to complete.

removal'otjthe charge from. the, cup. Thisoperation usually,takesf1om 3 tow 8 hours, vdepending. uponlocalconditionsof heating during reduction.

Aiterthecharaeis leachedpout ofthe cup, the. wooden block, molybdenumcub, and' cooling coil, are removedyand Athepovvder allowedto settle for about 20;l minutes. The supernatant liquid is pouredandV about 3jliters of water, added, plus equal-volume ofv glacial'acetic acid, and stirringis Ycontinued forabout 1-hour with the propelierZof the stirring apparatus well down into the jar toY insure maximum agitation, as represented xin Fig. Thepowderis then allowed` to settle, for about-lminutes and the supernatant liquid pouredo.

The powder inthevbottom of the container is then Washed'-vvith water, using 4 to 5 liters per.

.vasli,V stirringrfor 5' minutes, and settling for l5,

minutes between pour ois. peated 9 or lOtirnes.

DuringV the, rst washings, thiev supernatant liquid'v is cloudy due to, the presence ofnes. These areinotl lterable andare discarded. As"

This operation is rethe supernatant liquid becomes clearer, a white turbidity appears which is probably due to the reaction of the acid and water on very ne particles. With continued washing, this cloudinees disappears, and when this point is reached the powder is thrown on Buchner funnel 33, as illustrated in Fig. 4, using suction as applied to tube 35i of ilask 35. A relatively coarse iilter paper is preferably used in the funnel, the tubulation 33 of which passes through a cork 3? in the neck of flask 35. The powder is washed with water until the iltrate is clear, and then with alcohoi and ether in succession.

The metal powder, after removal from the Buchner funnel, may be dried and further treated and consolidated as ,described in Patent No. 2,446,062, previously referred to.

From the foregoing it will he seen that 1' have devised an improved method of manufacturing thorium in which the reaction is carried out in a transparent bulb so that the progress thereof can be visually ascertained. Ey virtue of carrying out the reaction in a closed container and in an inert gas atmosphere, the product is protected from deterioration as the inert gas can neither escape during the reaction, nor air or other gas enter the container during cooling.

Although a preferred embodiment of my invention has been described, it will be understood that modifications may be made within the spirit and scope of the appended claim.

I claim:

The method of manufacturing thorium comprising mixing a compound thereof selected from the group consisting of the chloride, the oxychloride, and mixtures thereof, with granulated distilled calcium in the proportion of about 70 parts by weight of the former to about 34 parts by weight of the latter, placing said mixture in a cup of moylbdenum, supporting said cup on a refractory insulator which rests upon a cooled metal plate, placing a molybdenum cover on said cup, placing a glass bell jar over said covered cup, sealing said jar to said plate, exhausting said jar to a high degree of vacuum, admitting inert gos to said jar to a pressure of about three-quarters of an atmosphere, placing a high-frequency coil around said jar, energizing said coil and slowly heating said cup to from 11.00 C. to 1200 C. for about iteen minutes to melt the calcium and reduce the thorium compound to metal powder, cooling and removing said cup, dissolving the excess oalcium, calcium chloride, and calcium oxide by means of dilute acetic acid, allowing the thorium powder as removed from said cup to settle, decanting the liquid therefrom, ua:hing the powder until cloudiness in the wash water disappears, ltering said powder with suction, Washing with water until the filtrate is clear, washing with alcohol, washing with ether, and drying.

WILLIAM C. LILLIENDAHL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,573,083 Marden et al Feb. 16, 1926 1,646,734 Marden I Oct. 25, 1927 OTHER REFERENCES Industrial & Engineering Chemistry, vol. 18, No.2 (1926) pages and 116.

Industrial & Engineering Chemistry, vol. 19, No. 1 (1927), pages 97 and 98.

Zeitschrift fur Anorganische Chemie, vol. 87, (1914), pages 211-216. 

